Web applications isn't that hard, it's pretty simple actually. You don't need RAD to create web UI. Just learn HTML and CSS with a little bit of JS (mostly needed for ajax transaction and live data updating) will do. Once you know how to deal with them (the trio HTML, CSS, and JS), it's pretty easy to create beautiful web UI by yourself.
I've been making web apps using Free Pascal (no Lazarus IDE) since about 15+ years ago, long before FPC provided fpWeb. I created my own web framework from scratch. No external frameworks like everybody is talking today needed. In my opinion, those frameworks make web app making unnecessarily complex and bloated. They also make web app programming looks hard and complicated. Yes, including fpWeb too.
REST is basically just another way communicating data through HTTP protocol. The front-end part of your app sends an HTTP request (either GET or POST or any other HTPP request methods) in known formatted data (either JSON or XML) and the back-end part of your app returns the data being requested in known formatted data as well (JSON or XML). It's still obey the basic HTTP communication mechanism, there's nothing actually new.
Using external framework make you dependent to it in long term, or you're vendor locked-in so to say. It makes you powerless when the framework is unavailable to you. If you let yourself invest your time a bit, say 1-2 weeks, to study HTML, CSS, and JS then you could build your great web app by yourself. I believe a smart and experienced programmer like @tatamata could master them easily in no time. Especially since now FPC also has pas2js that would cover the JS part.
Well… happy coding then.